Antenna coupling system



April 22, 1952 C. J. MILLER ANTENNA COUPLING SYSTEM Filed June 29, 1949TRANSMITTER TRANSMITTER WITNESSES:

INVENTOR Coleman J. Miller.

ATTORNEY Patented Apr. 22, 1952 ANTENNA COUPLING SYSTEM Coleman J.Miller, Catonsville, Md., assignor to Westinghouse Electric Corporation,East Pittsburgh, Pa., a corporation of Pennsylvania Application June 29,1949, Serial No. 101,942

This invention relates to antenna systems, and it has as an object theprovision of an antenna system which can be used efficiently at twodifferent frequencies.

Ordinarily where two carrier waves having different frequencies aretransmitted from one location, it is customary, for efficient operation,to use a separate antenna system for each frequency. While so-calledband antenna systems have been designed for use with differentfrequencies, in such systems the impedances of the antennas have beenmatched by circuits connected in shunt to the antennas, for matching theimpedances of their associated transmission lines at the differentfrequencies for preventing reflection losses and the formation ofstanding waves on the lines. For many duties such a broad-band system isnot as suitable for the efficient transmission of two frequencies asseparate antenna systems matched to the two frequencies. It has alsobeen proposed to use a single antenna for the transmission of severalfrequencies, and to manually adjust the physical length of the antennaso as to match the different frequencies. While such antennas are moreefficient than those used in broad-band antenna systems, theircomplications and their inability to handle efficiently, thesimultaneous transmission of two frequencies, prevents their use formany duties.

This invention provides for the efiicient use of a single antenna withtwo different frequencies. The antenna is a dipole, the length of whichis such that it is resonant at a frequency midway between the twofrequencies with which 5 Claims. (Cl. 250-33159) an antenna which can beefficiently used simulwave sections of transmission lines as coaxialinit is to be used. A parallel tuned circuit which also i resonant atthe frequency to which the dipole is resonant, is placed in series witheach of the two transmission lines connected to the dipole. At thehigher of the two frequencies, the reactance of the dipole will beinductive, and the reactance of the tuned circuits will be capacitive,the total reactance being zero. At the lower of the two frequencies, thereactance of the dipole will be capacitive, and the reactance of thetuned circuits will be inductive, the total reactance being zero. Thusthe antenna is matched to each of the two frequencies.

A feature of the invention is that it provides an antenna which can beefficiently used simultaneuously with two different frequencies.

Another object of the invention is to provide an antenna for use withtwo frequencies and having zero reactance at each frequency.

Another object of the invention is to provide nor conductors, and whichform parallel tuned circuits in series with the antenna and thetransmission lines.

Referring now to Fig. l, the lower frequency transmitter I!) whichoperates at, for example, a carrier frequencyof me. is connected throughthe filter H to the transmission lines l2. The transmission lines areconnected through the parallel-tuned circuits l3 consisting of theinductors l4 shunted by the capacitors 15, to the quarter-wave arms 16of the half-wave, dipole antenna l1.

The higher frequency transmitter I8 which operates at, for example, acarrier frequency of 150 me, is connected through the filter l9 to thetransmission lines l2.

The filters II and I9 are band pass filters which pass only thefrequencies of the carriers and their sidebands, of the transmitters Illand I8 respectively.

The dipole antenna H is cut to resonate at a frequency of me. which isapproximately midway between the carrier frequencies of the twotransmitters. The parallel tuned circuits I3 are also tuned to resonateat the mid-frequency of 125 mc., and for accomplishing this, theinductors [4 may each have an inductance of .02 microhenry, and thecapacitors l5 each may have a capacity of 80 micromicrofarads.

In operation, at the higher carrier frequency of the transmitter [8, thereactance of the dipole antenna will be inductive, and the reactance ofthe parallel-tuned circuits l3 will be correspondingly capacitivewhereby the total reactance is zero. At the lower carrier frequency ofthe transmitter I ii, the reactance of the dipole antenna will becapacitive, and the reactance of the parallel-tuned circuits 13 will becorrespondingly inductive whereby the total reactance will be zero. Thusthe single antenna offers zero reactance at the carrier frequency ofboth transmitters, and is equally effective at both frequencies.

The two transmitters can be operated simultaneously without interactionor, of course, can be operated alternately.

There is no broad-band effect except that inherent in the physical sizeof the dipole. A dipole having a large cross-sectional diameter will bebroader banded than one having a smaller diameter.

Fig. 2 of the drawing illustrates a conventional dipole constructionwhich may be used in the practice of this invention, the dipoleincluding the parallel-tuned circuits 13 illustrated by Fig. 1. Thequarter-wave, dipole arms 15 are tubular, and are closed at their outerends 20 and are open at their inner ends 2|. The coaxial innerconductors 22 are shorted at their outer ends to the outer ends 20 ofthe .dipole, and are connected at their inner ends to the transmissionlines 12. The radiating surface of the antenna is the outer surface ofthe dipole, and the parallel resonant circuits corresponding to thecircuits 13 of Fig. 1, are formed by the proper sizing and spacing ofthe opposing outer surfaces of the inner conductors 22 and the innersurfaces of the dipole arms, l6.

While the invention has been described in connection. with radiotransmitters, it. can also be used with. radio receivers.

I claim as my invention:

1. An antenna system for use with two radio frequency sources. havingdifferent frequencies, comprising a dipole antenna. resonant. at afrequency midway between said frequencies, a pair of transmission linesfor connecting said. frequency sources to said: antenna, and meansforming parallel-tuned .circuits in series with said transmission linesand said antenna, said circuits being resonant at said midway frequency.

2'. An antenna system as claimed in claim 1 in which the dipole arms arecoaxial conductors shorted at their outer ends. and are-connected to thetransmission lines by inner conductors, and in which the parallel-tunedcircuits are-formed by the opposedouter surfaces of the inner conductorsand the inner surfaces of the dipole arms.

3. An antenna system as claimed in claim 1 in which the parallel-tunedcircuits areshunt connected inductors andcapacitors connected in tennaresonant at a frequency midway between.

said frequencies, a pair of transmission lines connected to saidtransmitters, and means providing parallel-tuned circuits resonant atsaid midway frequency connected in series with said lines and the armsof said antenna.

COLEMAN J. MILLER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,545,041 Doring July 7, 19251,610,073 Alexanderson Dec. 7, 1926 1,730,903 Schmidt et al Oct. 3, 19291,969,328 Roosenstein Aug. 7, 1.934 2,019,341 Dome Oct. 29, 19352,128,400 Carter Aug. 30-, 1938 2,284,434 Lindenblad May 26, 19422,311,364 Buschbeck et a1. Feb. 16, 1943 2,480,172 Willoughby Aug. 30,1949 2,490,957 Gluyas, J-r Dec. 13, 1949 2,493,514 Wehner Jan. 3, 1950FOREIGN PATENTS Number Country Date 157,060 Great Britain Dec. 18, 1920534,894 France Apr. 4, 1922 OTHER REFERENCES Two Transmitters on OneAerial, by Morton and Whitehead; Electronic Engineering, May 1948, pages157 to 159.

